332 
DUNCAN S. JOHNSON 
and thus ultimately gives rise to the characteristic, short-stalked, 
orbicular bract. It has an epidermis sprinkled with oil cells and 
hydathodes, and within is a short, simple branch from the vascular 
bundle of the axis (figs. 25, 56). This bract reaches essentially its 
mature size, 125 )U in diameter, before the embryo sac of the same 
flower is ripe (figs. 22, 56, 78). As the fruit matures the bract shrivels 
somewhat but remains attached to the axis, even after the fruit has 
fallen. It is evident that this bract does not, except in the very earliest 
stages of the flower, protect the latter from desiccation or other injury 
(figs. 22, 56, 78). This subtending bract of the flower plays a far 
more important part in shielding the young flower in the cases of 
the more xerophytic species of Peperomia, as we shall have occasion 
to point out in a later paper. 
C. The Development of the Stamen, Microspore and Pollen 
Tube. 
The stamen of Peperomia hispidula arises by the outpushing of a 
group of 8 or 10 periblem cells on each side of the young floral bract, 
and below the carpel which is developing at the same time just above 
the bract (figs. 25, 26, 27). When the group of hypodermal cells at 
the end of the young stamen has reached the number of about 40 or 
50, there appear, in two regions where the microsporangia are to be 
formed, numerous periclinal walls in these cells (figs. 29, 30) . The inner 
of the two layers thus formed gives rise to the definitive archesporium 
or sporogenous layer of the microsporangium. The outer layer is a 
primary parietal layer, the cells of which soon divide by periclines into 
two series. The outer series of cells thus formed constitutes the 
fibrous layer or endothecium of the mature anther wall. The inner 
of the two series divides once more by periclines forming the single 
tapetal layer within and an outer layer, lying next the endothecium, 
which becomes the innermost layer of the wall of the mature anther 
(figs. 33, 34). In the mature microsporangium the epidermal cells 
have thin, uncutinized and collapsed outer walls. The endothecium 
of the mature anther is about 20 ^ thick, and consists of poly- 
gonal cells, 20 to 25 iJL in diameter, with thin outer walls and thick 
inner ones. The lateral walls have 15 or 20 rib-like thickenings, which 
are really radial projections of the basal or inner wall (fig. 34). The 
nuclei of these cells, like those of the epidermis, degenerate and flatten 
out as the anthers ripen. The cells of the layer next within the endo- 
